This invention relates to catheter shaft design. In particular, the invention relates to a proximal shaft design for intravascular catheters and catheters that incorporate the proximal shaft design. The proximal shaft design is resistant to kinking, maintains sufficient stiffness and can be incorporated into a low profile catheter.
Catheters are used to place various treatment materials, drugs, and devices within remote target regions of the human body. Catheters designed to traverse the pathways to these target regions typically provide the desired balance between the flexibility required to allow passage of the catheter tip through the tortuous bends of the increasingly narrow blood vessels and the stiffness required to allow the operator to push the catheter tip from the proximal end as the catheter is advanced into the body. The catheter shaft usually has at least two sections, the distal shaft section and the proximal shaft section. The proximal shaft section is usually stiff and provides for the support and push of the catheter during advancement. The distal shaft section on the other hand is usually more flexible and provides for tracking through the vascular pathways. A catheter may have additional sections defined as intermediate shaft sections that provide a gradual transition from the stiffer proximal shaft section to the more flexible distal shaft section.
Some catheters are used to treat coronary vessel narrowing (coronary vessel stenosis). Percutaneous transluminal coronary angioplasty (PTCA), also known as balloon angioplasty, is one of the techniques used for treating stenosis of the coronary arteries. Patients treated by PTCA, however, may suffer from a high incidence of coronary vessel narrowing subsequent to treatment (restenosis), with a significant number of patients requiring treatment for restenosis. In a typical PTCA procedure a guiding catheter is percutaneously introduced into the cardiovascular system of a patient through the brachial or femoral arteries and advanced through the vasculature until the distal end is in the opening of a coronary artery (ostium). In order to reduce the risk of complications, excessive bleeding for example, the physician usually uses a small diameter guiding catheter of 6F or less (F=1 french which is 0.013 inch). More recent devices and procedures for preventing restenosis employ a radiation catheter to deliver a radiation source to minimize or eliminate the cell proliferation implicated in the restenosis process. Radiation catheters are generally larger in diameter than typical dilatation catheters and are one means to deliver and maintain the radiation source in the treatment area.
Many catheters are designed to have the smallest cross-sectional diameter possible to minimize the diameter of guiding catheter needed, thus minimizing the size of the puncture or incision needed to gain access to the body lumen of interest. Additionally, a lower profile catheter may permit access to smaller vessels. Currently, to achieve a minimal profile, provide sufficient stiffness, and maintain sufficient kink resistance, rapid-exchange dilatation catheters utilize stainless steel hypotubes for the proximal catheter shaft. These hypotubes provide the desired properties for a rapid exchange proximal shaft for designs which only require a single inflation lumen with an inner diameter of between 0.010 inch and 0.020 inch. As the inner diameter of the hypotube is increased beyond 0.020 inch, the tube becomes highly susceptible to kinking. Kink resistance of these larger diameter tubes can be improved by increasing the wall thickness of the tubing, but this quickly results in a tube which is too stiff to function as a catheter shaft. Also, the rough, metal inner surface of a typical hypotube, while adequate for use as an inflation lumen, is not appropriate for use in delivering a therapeutic tool, such as a radiation source wire. Some, but not all, of the limitations of a stainless steel hypotube can be overcome through the use of a superelastic nickel-titanium alloy. However, the cost of these super-elastic materials is prohibitive and the inner surface characteristics are not appropriate for delivery of source wires. Thus, these inherent properties of a metal hypotube make it inappropriate for use in designs which require more than a relatively small inflation lumen, that is, inappropriate for designs such as radiation catheters.
An alternate rapid exchange catheter shaft design known in the art is the use of round polymer tubing(s) combined with a metal reinforcing mandrel. While these designs utilizing round extrusions can meet the functional requirements of catheters such as radiation centering catheters, these designs result in large shaft dimensions.
The catheters used in intravascular procedures, particularly to deliver a radioactive source to a target area within the body lumen, may have the following properties for improved performance: a) a source lumen with a lubricious lining b) an inflation/deflation lumen c) sufficient stiffness to allow for support and advancement of the distal end of the catheter d) a resistance to kinking, and e) a minimal cross-sectional area to allow the shaft and guide wire to fit within the guiding catheter with ample space to allow dye injection and other manipulation. A catheter with these general properties should permit access to smaller vessels within the body and improve catheter performance.
One approach to optimizing a catheter is to minimize the thickness of the shaft walls by using a shaft material with increased stiffness. The problem encountered with this approach is that the propensity to kink is increased as the shaft wall thickness is decreased and the material stiffness is increased. The design of a proximal catheter shaft typically balances the need for a small diameter shaft with the requirements for shaft stiffness, while limiting the propensity to kink during catheter advancement.
The current invention addresses the need for a low profile proximal shaft design that provides support and kink resistance during use, as well as other requirements described in the following description.
The invention is directed to providing a stiff, kink resistant proximal shaft section for a catheter and catheters that incorporate such a proximal shaft. The proximal shaft section design comprises radially extending ridges running longitudinally along the proximal shaft section with inset regions positioned between the radially extending ridges.